The substitution of one metal ion in a Cr-based molecular ring with dominant antiferromagnetic couplings allows the engineering of its level structure and ground-state degeneracy. Here we characterize a ${\mathrm{Cr}}_7\mathrm{Ni}$ molecular ring by means of low-temperature specific-heat and torque-magnetometry measurements, thus determining the microscopic parameters of the corresponding spin Hamiltonian. The energy spectrum and the suppression of the leakage-inducing $S$ mixing render the ${\mathrm{Cr}}_7\mathrm{Ni}$ molecule a suitable candidate for the qubit implementation, as further substantiated by our quantum-gate simulations.

An unusually large magnetocaloric effect for the temperature region below 10 K is found for the ${\mathrm{Fe}}_{14}$ molecular nanomagnet. This is to large extent caused by its extremely large spin $S$ ground state combined with an excess of entropy arising from the presence of low-lying excited $S$ states. We also show that the highly symmetric ${\mathrm{Fe}}_{14}$ cluster core, resulting in small cluster magnetic anisotropy, enables the occurrence of long-range antiferromagnetic order below $T_N=1.87\mathrm{K}$ .

We characterize supramolecular magnetic structures, consisting of two weakly coupled antiferromagnetic rings, by low-temperature specific heat, susceptibility, magnetization and electron paramagnetic resonance measurements. Intra- and inter-ring interactions are modeled through a microscopic spin-Hamiltonian approach that reproduces all the experimental data quantitatively and legitimates the use of an effective two-qubit picture. Spin entanglement between the rings is experimentally demonstrated through magnetic susceptibility below 50~mK and theoretically quantified by the concurrence.

By substituting one ${\mathrm{Cr}}^{\text{3+}}(\mathrm{s}\text{=3/2)}$ with ${\mathrm{Cd}}^{\text{2+}}(\mathrm{s}\text{=0)}$ in molecular octanuclear rings, a diluted ensemble of identical nanomagnets with a $\text{S=3/2}$ ground state, weakly split in zero field, is obtained. The lattice contribution and the essential parameters of the spin Hamiltonian of these uncompensated antiferromagnetic cyclic spin systems are determined by fitting specific heat data between 0.4 and 20 K in magnetic fields up to 7 T. Different entropy contributions are evaluated and results suggest a possible way of engineering molecular magnets to exploit low temperature magnetocaloric effect.